Therapeutic embolization or occlusion of blood vessels may be used to treat a variety of vascular and non-vascular conditions including cerebral and peripheral aneurysms, ateriovenous malformation, uterine fibroids and various tumors. One commonly used agent for embolizing blood vessels is the embolic coil, a permanently implanted coiled wire structure which, when implanted into a blood vessel, occludes the vessel by causing thrombosis where it is deployed. Embolic coils may have different lengths and/or cross-sectional diameters, in order to fit into and occlude vascular structures of varying sizes. In use, the coils are delivered through a microcatheter in a narrow-diameter elongated configuration (e.g. to fit within a 3 Fr (or 1 mm diameter) catheter lumen). Once deployed into the vessel, the coil may assume a complex 3-D shape such as a helix, a spiral, a J-shape, or a birds-nest shape, and may include thrombogenic fibers or bundles of fibers along its length. Embolic coils are highly flexible, and can be delivered through narrow or tortuous vascular structures, but when occlusion of relatively vascular structures is desired, multiple coils may be necessary to achieve full occlusion, which in turn may increase the time and cost required for a therapeutic embolization procedure.
Another common occlusive agent is the occlusion plug, typically a braided structure comprising multiple strands of a shape memory material, most often nitinol. The occlusion plug, like the embolic coil, is capable of collapsing to a narrow diameter (for example to fit within the lumen of a delivery catheter) and then expanding to a relatively larger diameter which occludes the vessel of interest, but a typical plug generally occupies a larger volume and expands to a larger diameter than a typical embolic coil. This increased size allows occlusion plugs to efficiently occlude large-gauge vessels and vascular structures. In addition, occlusion plug procedures are generally less expensive, per-unit, than embolic coils, owing to the lower cost of materials for plug procedures (which typically require only a single device) versus coils (which may require implantation of multiple coils). However, due to their larger size, occlusion plugs are generally not able to be delivered through tortuous vascular structures, and typically require larger-bore catheters (e.g. 5-8 Fr, or 1.667-2.667 mm diameter) for delivery.